1. Field of the Invention
The present invention relates to a method and a jig for processing a cylinder block making up of an internal-combustion engine such as an automobile engine, as well as the cylinder block.
2. Related Art
A cylinder block making up of an internal-combustion engine such as an automobile engine, as a general construction thereof, is provided with a cylinder bore, which slidably incorporates a piston as a cylindrical aperture portion, a cylinder head mounting surface (hereinafter, referred to as “a head mounting surface”) onto which a cylinder head is assembled, as an open surface of the cylinder bore. A fastening means (a head bolt) such as a bolt is used in the assembly of the cylinder head onto the head mounting surface. In other words, the head bolt penetrates the cylinder head and is threaded into a blot hole as a female threaded portion provided with the cylinder block, so that the cylinder head is tightly fixed in the cylinder block.
The bolt hole into which the head bolt is threaded in the fixation of the cylinder head in the cylinder block is provided on the periphery of the cylinder bore on the head mounting surface. Specifically, four bolt holes are provided at substantially equal spaces on the periphery of the cylinder bore. Briefly, in this case, for example, in an in-line four-cylinder engine installed on the automobile or the like, two bolt holes out of four bolt holes in line are shared between the adjacent cylinder bores, so that a total of ten bolt holes are provided.
Due to the above construction, a deformation of the cylinder bore (a bore deformation) is caused, during the assembly of the cylinder head into the cylinder block, and at the time of actual working of an engine composed of the cylinder block. In other words, the bore deformation at the time of actual working of the engine includes a deformation caused during the assembly of the cylinder head (hereinafter, referred to as “an assembly deformation”) and a deformation caused by a heat load at the time of actual working of an engine. A circularity of the cylinder bore is determined by these bore deformations.
Here, the bore deformation will be concretely described with reference to FIG. 12. In FIG. 12, FIG. 12 (a) is a diagram of a single part state (a state that is not assembled), FIG. 12(b) is a diagram of the bore deformation during the assembly or at the time of actual working of the engine.
As shown in FIG. 12, as an example of providing the cylinder bore with a bolt fastening portion for fixing the cylinder head to the cylinder block, four bolt fastening portions 110 in one cylinder bore 104 are provided at substantially equal spaces on the periphery of the cylinder bore 104. In the respective bolt fastening portions 110, the head bolt 111 is threaded into a bolt hole 112.
As shown in FIG. 12 (a), in the single part state that the cylinder head is not fixed by the fastening of the head bolt 111 threaded into bolt hole 112, as the tightening force (the fastening power) by the head bolt 111 is not added to the cylinder block, the deformation of the cylinder block is not caused due to the action of the fastening power, so that the cylinder bore 104 does not receive the deformation.
As shown in FIG. 12 (b), during the assembly in the condition that the cylinder head is tightly fixed into the cylinder block, the tightening force by the head bolt 111 acts on the cylinder block, whereby the tightening force causes the deformation to the cylinder block, thereby leading to the assembly deformation. The assembly deformation is caused due to the fact that the bore upper surface (the peripheral portion of the cylinder bore 104 in the head mounting surface) is strongly pressed by the fastening of the head bolt 111.
Therefore, the periphery of the bolt pressed particularly strongly has a larger deformation, and in the construction that four bolt fastening portions 110 are provided at approximately equal spaces on the periphery of the cylinder bore 104 as the present example, the deformation that the portion of the phase (herein after, referred to as “the bolt phase”) corresponding to the bolt fastening portions 110 dwindles inward (expands relatively inward) is caused, in the cylinder bore 104 (see an arrow in FIG. 12 (b)). Consequently, as shown in FIG. 12 (b), in the assembly deformation, the cylinder bore 104, which was a round shape in the planar view, deforms a cross-like figure (so-called a fourth-order deformation). In the bore deformation caused by the heat load at the time of actual working of the engine, the cylinder bore 104 deformed by the assembly deformation receives the deformation that the cross-like figure thereof is emphasized.
The above-mentioned bore deformation causes the deterioration in the circularity of the cylinder bore. The deterioration in the circularity of the cylinder bore leads to the increase of the friction (the sliding resistance) accompanying the sliding of the piston onto the cylinder bore. The increase of the friction causes to the output limitation of the internal-combustion engine, the deterioration of the fuel consumption or the like.
Specifically, a piston is attached to a piston ring, which slidably contacts the cylinder bore, and the deterioration in the circularity of the cylinder bore causes to the reduction of the sealing characteristics by the piston ring, at the portion where the cylinder bore changes from the perfect circle to the large diameter (the portion expanding the diameter), thereby increasing an engine oil consumption and a blow-by gas due to the leaching. This situation can be prevented by increasing a tension of the piston ring (the expanding force) (by making the tension of the piston ring the high tensile force), so that even the portion changing to the large diameter in the cylinder bore can secure the minimum pressing force by the piston ring. However, the high tensile force of the piston ring leads to the increase of the friction in the whole cylinder bore.
In this regard, in order to restrain the bore deformation at the time of actual working of the engine, the processing method, which can aim for the circularity of the cylinder bore at the time of actual working of the engine, by preliminary adding the deformation in the direction opposite to the bore deformation at the time of actual working of the engine to the cylinder bore, is required, when the finish processing (such as the honing process) so as to obtain the given circularity of the cylinder bore is performed.
Briefly, when the cylinder head is assembled into the cylinder block after the finish processing for the cylinder bore has been performed, the inverse deformation need to be caused so that the cylinder bore becomes a perfect circle, due to the heat load during the assembly of the cylinder head and at the time of actual working of the engine. In other words, the inverse deformation need to be caused, so that the cylinder bore deformed due to the assembly deformation and the deformation by the heat load becomes a perfect circle, at the time of actual working of the engine. For this reason, in the single part state after the finish processing for the cylinder bore has been finished, the inverse deformation as shown in FIG. 13 need to be added to the cylinder bore.
Thus, conventionally, as the processing method that can add the inverse deformation in the single part state after the finish processing for the cylinder bore has been finished, the processing method using a dummy head is known (for example, see JP2004-243514A).
The dummy head is a jig for processing different from the cylinder head assembled as an actual product, and it is assemble into the cylinder block by a head bolt as with the cylinder head, during processing of the cylinder bore. The condition that the cylinder head is assembled into the cylinder block is simulated with the dummy head. Specifically, due to the assembly of the cylinder head into the cylinder block, the predetermined tightening force equivalent to the tightening force with the assembly of the cylinder head is added to the cylinder block, thereby adding the assembly deformation to the cylinder bore. In this situation, the finish processing for the cylinder bore is performed, and the dummy head is removed after the finish processing, so that the inverse deformation is added to the cylinder bore, due to the restoration action accompanying the cancel of the tightening force. The cylinder head is assembled into the cylinder block which the inverse deformation is added to the cylinder bore, thereby restraining the deterioration in the circularity of the cylinder bore due to the bore deformation (the assembly deformation) caused by the tightening force during the assembly of the cylinder head.
However, the processing method using the dummy head requires the respective process of fastening (assembling), disassembling, (removing), washing, delivering or the like of the dummy head, thereby leading to the complexity of process for processing the cylinder block. It is not preferable to complicate the working process, for the improvement of the mass productivity. The processing method using the dummy head requires a preparation of a considerable of dummy heads considering the production cycle time, and equipments for the respective process such as the assembly of the dummy head or the like, thereby increasing the cost.
Consequently, it is an object of the invention to provide a method and a jig for processing a cylinder block, as well as the cylinder block, which can add the deformation in the direction opposite to the bore deformation caused at the time of actual working of the engine to the cylinder bore after the finish processing, so as to restrain the deterioration in the circularity of the cylinder bore at the time of actual working of the engine, without the complexity of the working process and the increase in cost caused by using the jig for processing, in the finish processing for the cylinder bore in the cylinder block.